The business executive who executed his family before setting their rented home ablaze had not complained about any financial difficulties, his father-in-law said today.

Darrin Campbell, 49, was found dead alongside his wife Kimberly and teenage children in a Florida mansion.

The financial expert is believed to have systematically shot his family in the head with a .40-caliber handgun before starting the blaze at the home of former tennis star James Blake.

His wife's devastated family spoke out as CCTV emerged of Campbell buying an 'exceedingly large' amount of fireworks and gas canisters in the days before the house went up in flames.

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Executed: Police revealed today that Darrin Campbell, left, shot wife, Kimberly, right, in the head with his .40-caliber handgun he bought last year. He killed his two children in the same way

'Perfect': Kimberly's father told MailOnline that his daughter hadn't told him about any financial troubles that may have pushed him to breaking point. The Campbells had moved to the property two years ago to be nearer the private school Colin, 19, pictured left at prom and right on the baseball field, attended with his sister, Megan

Tragic: Megan, 16, pictured left and right,
attended Carrollwood day school. She had just won an award days before the murders. Friends as well as relatives have expressed utter shock over the killings

Shocked friends and family still coming to terms with the four deaths are mystified why Campbell would have gone on such a deadly rampage.

'I am hearing all the gory details and I can't believe it,' said Gordon Lambie, his father-in-law. 'Did he have financial worries? Not that I was aware of. I talk with my daughter all the time and she had never said anything before.

'All I know is that I have lost my family, my daughter, my grandchildren. It is all too much.'

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Mr Lambie, 84, who lives in Michigan, added that he was too frail to travel to Florida to find out more details. 'I am looking after my wife and have my own health problems. I can't believe what I am hearing.'

Investigators are pouring over Campbell's bank accounts and financial records to see if they provide a clue to what pushed him over the edge.

After almost 18 months out of work he landed a job six months ago as Chief Operating Officer of a digital storage company in Tampa.

He had previously held senior positions with several south Florida companies but no longer for more than three years with any of them.

Haunting video: A surveillance video has emerged showing Darrin Campbell dressed in a dark-grey T-shirt and shorts buying a pile of fireworks last Sunday

Evidence: The surveillance footage was recorded inside the store Phantom Fireworks

The firecrackers seen in Campbell's shopping cart in the video were reportedly used to start a fire in his home Wednesday

Business as usual: Store clerk Michael Muti (right) who handled the transaction Sunday recalled that Campbell seemed 'normal and chatty'

Star rental: The Campbell's rented the home from tennis star James Blake, left. Campbell, right, had had a serious of high-profile and senior jobs in various industries. He had apparently been out of work for a year but had recently secured another good job six months ago as the COO of a digital storage company in Tampa

In many other previous murder-suicides financial or marital problems have been cited for the reason the killings taking place.

Family members said Campbell and his 51 year old wife had a 'strong marriage'. Campbell's mother Mary said they had 'everything to live for' and were a perfect family.

The investigation is likely to focus on Campbell's financial situation.

Local realtors estimate Campbell would have been paying $6,000 a month to rent out the 5,000 sq ft home from former tennis star James Blake.

The family moved into the rented home so that the children could be near to their private school after selling their previous $750,000 home for a profit.

He also had school fees for son Colin,19, and daughter Megan,16, of more than $35,000 a year.

At a press conference on Friday, Hillsborough County Sheriff's Col. Donna Lusczynski said the sheriff's office had not been investigating Campbell before the killings and did not know of any other agencies that may have been investigating him. Campbell had no criminal record before his death.

Investigators confirmed they looking into the family's finances and going through records found in the home, Lusczynski said. but a search of public records shows no sign of financial strain on the family.

Meanwhile, A surveillance video was released late Thursday showing Darrin Campbell dressed in a dark-grey T-shirt and shorts placing stacks of fireworks into a shopping cart at Phantom Fireworks.

The firecrackers that Campbell bought reportedly surrounded
the bodies and apparently started the fire that engulfed the two-story,
five-bedroom home.

Remains: This aerial photo shows the burned out home owned by James Blake on Thursday, May 8, a day after it was set alight

Sinister: Fireworks were found strewn around the house and police say an accelerant - probably the gas canisters he bought - were used to start the blaze

Fire: The blaze was so ferocious on May 7 that firefighters could not get in to examine the grisly scene until the next day

The nine-minute silent clip depicts the married father of two emptying his full cart at the cash register.

At
one point, Campbell is seen ducking back into an aisle to pick up more
pyrotechnics before handing the cashier $650 in cash for his purchase.

Store clerk Michael Muti who handled the transaction Sunday recalled Campbell as being 'normal and chatty.'

'He said he was shopping early for fireworks for the Fourth of July,' Muti said.

Neighbors described hearing the fireworks go off as the house burned.

'Geez. What is that popping noise?' a male neighbor said on a 911 call.

Another 911 caller, a security manager for the gated community, told dispatchers the fire was in the house's garage.

Firefighters
have described the scene inside the burnt-out mansion as 'unusual' with
fireworks littered through the five-bedroom home rented from former
tennis player Blake, who was ranked fourth in the world in 2006.

Neighbors alerted the emergency authorities when they saw flames leaping from the home. There was no 911 call made from within the property.

According to her Twitter, Megan won an academic award at the school just a day before the deaths.

Darrin
and Kimberly met in Lansing, Michigan, when they both worked as
legislative aides in the state legislature. Kimberly Campbell had
graduated from Central Michigan University and Darrin Campbell had an
MBA from the University of Michigan, Lambie said.

Away: Blake, pictured with his wife, Emily, was reportedly at their Connecticut residence when the fire broke out

They
had lived in San Antonio, Texas, where Darrin Campbell was an executive
with Pearl Brewing Company before they moved to the Tampa area around
2001 so he could take a job with Anchor Glass Container Corp.

They
sold their previous home but wanted to live in a place close to their
children's school, so they signed a two-year lease for Blake's home,
which was close enough for the teens to walk to school, Lambie said.

Police
said the family had been living there for about two years. Neither
deputies nor the Department of Children and Families had been called to
the home, officials said.

A former neighbor, George Connley, said they were a nice family. He said that Kimberly Campbell was 'sophisticated and classy.'

'We
know nothing of any problems,' Connley said. 'The kids were outstanding
children. This is very difficult to put our arms around.'